Clinical and pathologic features of cardiac rhabdomyomas in 36 patients are described, including 7 patients in whom tumors were examined by electron microscopy. It is concluded from these studies that rhabdomyomas of the heart are definitely derived from cardiac muscle cells and probably represent hamartomas rather than true tumors. BIBLIOGRAPHIC REFERENCES: Fenoglio, Jr., J.J., McAllister, Jr., H.A., and Ferrans, V.J.: Cardiac rhabdomyoma: a clinicopathologic and electron microscopic study. Am J Cardiol 38: 241-251, 1976.